The present invention relates to a method for forming an interlayer insulating film and, more particularly, to a method for forming an interlayer insulating film having a low dielectric constant, which is necessary for a highly-integrated semiconductor device. A progress in high integration regarding the semiconductor device in recent years has resulted in a narrower interval between wiring lines. As the narrowed interval between the wiring lines causes an increase in capacitance between the wiring lines, a request has been made for formation of an interlayer insulating film, which has a low dielectric constant.
With recent progresses in high integration of an LSI device, the wiring line has been micronized and multilayered. There has also been an increase in capacitance between the wiring lines. Such an increase in capacitance has caused a great reduction in an operating speed. Thus, improvement in this regard has been strongly demanded. As one of improvement measures, a method for reducing capacitance between the wiring lines has been studied. This method uses an interlayer insulating film, which has a dielectric constant lower than that of SiO2 currently used for an interlayer insulating film.
Typical interlayer insulating films of low dielectric constants currently under study are {circle around (1)} an SiOF film, and {circle around (2)} an organic insulating film of a low dielectric constant. Description will now be made of these films.
{circle around (1)} SiOF Film
An SiOF film is formed by using source gas containing F and substituting Sixe2x80x94F bond for a portion of Sixe2x80x94O bond in SiO2. This SiOF film has a relative dielectric constant, which is monotonically reduced as concentration of F in the film increases.
For forming such SiOF films, several methods have been reported (see p.82 of monthly periodical xe2x80x9cSemiconductor Worldxe2x80x9d, February issue of 1996). Most promising among these methods is one for forming an SiOF film by using SiH4, O2, Ar and SiF4 as source gases, and by a high-density plasma enhanced CVD method (HDPCVD method). A relative dielectric constant of an SiOF film formed by this method is in a range of 3.1 to 4.0 (varies depending on F concentration in the film). This value is lower than a relative dielectric constant 4.0 of SiO2, which has conventionally been used for the interlayer insulating film.
{circle around (2)} Organic Insulating Film of Low Dielectric Constant
As an insulating film which has a lower dielectric constant (3.0 or lower) compared with the SiOF film, an organic insulating film of a low dielectric constant is now a focus of attention. Table 1 shows a few organic insulating films of low dielectric constants, which have been reported, and respective relative dielectric constants and thermal decomposition temperatures thereof.
However, the SiOF film is disadvantageous in that an increase in concentration of F in the film leads to a reduction in moisture absorption resistance. The reduced moisture absorption resistance poses a serious problem, because a transistor characteristic and adhesion of an upper barrier metal layer are affected.
Peeling-off easily occurs in the organic insulating film of a low dielectric constant, because of bad adhesion with a silicon wafer or the SiO2 film. Furthermore, the organic insulating film is disadvantageous in that heat resistivity is low since a thermal decomposition temperature is around 400xc2x0 C. The disadvantage of low heat resistivity poses a problem for annealing a wafer at a high temperature.
It is an object of the present invention to provide a method for forming an interlayer insulating film of a low dielectric constant, which has good moisture absorption resistance and heat resistivity. It is another object of the invention to provide a semiconductor device, which employs the above method.
Description will now be made of an interlayer insulating film of the present invention by referring to Table 2.
For formation of a porous SiO2 film of the present invention, TEOS, TEOS+O2 or TEOS+H2O is used as source gas. By performing plasma polymerization for such source gas, an Sixe2x80x94C film, an Sixe2x80x94Cxe2x80x94H film, an Sixe2x80x94Cxe2x80x94O film or an Sixe2x80x94Cxe2x80x94Oxe2x80x94H film is formed on a formed body. Then, by performing O (oxygen) plasma treatment for these films, C or H is oxidized in the film. C or H is oxidized in the film, and voids are formed in portions from which C or H has been discharged. Accordingly, a porous SiO2 film is formed. A porous SiO2 film can also be formed by using methylsilane (Si(CH3)H3), instead of TEOS.
For formation of a porous B(boron)-containing SiO2 film of the present invention, TEOS+B2H6, TEOS+B2H6+O2 or TEOS+B2H6+H2O is used as source gas. By performing plasma polymerization for such source gas, an Sixe2x80x94Cxe2x80x94B film, an Sixe2x80x94Cxe2x80x94Bxe2x80x94H film, an Sixe2x80x94Cxe2x80x94Bxe2x80x94O film or an Sixe2x80x94Cxe2x80x94Bxe2x80x94Oxe2x80x94H film is formed on a formed body. Then, by performing O (oxygen) plasma treatment for these films, C or H is oxidized in the film. C or H is oxidized in the film, and voids are formed in portions from which C or H has been discharged. Accordingly, a porous B-containing SiO2 film is formed. A porous B-containing SiO2 film can also be formed by using methylsilane (Si(CH3)H3) or trimethyl-siliruborate ({(CH3)3SiO}3B), instead of TEOS in source gas. Instead of B2H6 in source gas, TMB(B(OCH3)) or TEB(B(OC2H5)3) can be used to form a porous B-containing SiO2 film.
For formation of a porous F-containing SiO2 film of the present invention, TEOS+C2F6, TEOS+C2F6+O2 or TEOS+C2F6+H2O is used as source gas. By performing plasma polymerization for such source gas, an Sixe2x80x94Cxe2x80x94F film, an Sixe2x80x94Cxe2x80x94Fxe2x80x94H film, an Sixe2x80x94Cxe2x80x94Fxe2x80x94O film or an Sixe2x80x94Cxe2x80x94Fxe2x80x94Oxe2x80x94H film is formed on an object to be formed. Then, by performing O (oxygen) plasma treatment for there films, C or H is oxidized in the film. C or H is oxidized in the film, voids are formed in portions from which C or H has been discharged. Accordingly, a porous F-containing SiO2 film is formed. A porous F-containing SiO2 film can also be formed by using methylsilane (Si(CH3)H3), instead of TEOS.